Biodegradable plastics are of increasing industrial interest as replacements or supplements for non-biodegradable plastics in a wide range of applications and in particular for packaging applications. One class of biodegradable polymers is the polyhydroxyalkanoates (PHAs). These polymers are synthesized by soil microbes for use as intracellular storage material. Articles made from the polymers are generally recognized by soil microbes as a food source. There has therefore been a great deal of interest in the commercial development of these polymers, particularly for disposable consumer items. To date, however, PHAs have seen limited commercial availability, with only the copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) being available in appreciable quantities.
Although various PHAs are capable of being processed on conventional processing equipment, many problems have been found with the polymers. These include lack of processability in some situations, which can limit the commercial applications available for use of the polymer; molecular weight may be difficult to maintain. In addition, the crystallization kinetics of the polymer are poorly understood, and long cycle times are often required during processing of these polymers, further limiting their commercial acceptance.
PHA compositions containing high levels of 3-hydroxybutyrate monomer can have physical limitations such as brittleness and thermal stability issues at melt processing temperatures (e.g., those temperatures used in injection molding, sheet extrusion and blown film conversion), and the resultant products may not have an acceptable degree of toughness for many applications. Thus, a need exists for toughened PHA compositions.